This document claims priority and contains subject matter related to Japanese Patent Application No. 11-374270, filed on Dec. 28, 1999, and the entire contents of which are hereby incorporated herein by reference.
1. Field of the Invention
The present invention relates to an image reading device having a sheet-through mechanism for use in a scanner and an image forming apparatus, such as a copying machine, a facsimile, etc., and more particularly to an image reading device that increases reading throughput and that obtains quality image data by performing an image reading operation which satisfies user needs.
2. Discussion of the Background
In a background art image reading device which reads an image of an original document via a sheet-through mechanism, a white plate reading operation (i.e., a shading operation) has to be performed before reading the image of the original document. Consequently, loss of time, caused by a movement of a scanner carriage to the white plate, results. It has been considered to reduce the number of shading operations in order to increase reading throughput. However, it is preferable that the shading operation is performed each time an image of an original document is read because a shading waveform changes with a lighting period of time of an exposure lamp. For example, Japanese Patent Laid-Open Publications Nos. 8-9116 and 9-247395 describe technologies addressing the above-described problem.
According to Japanese Patent Laid-Open Patent Publication No. 8-9116, two white plates are provided. An image of an original document read by a first or a second image reading mode is converted to electric signals from optical signals using a photoelectric element. In the first image reading mode, the image of the original document placed on a platen is read. In the second image reading mode, the image of the original document fed by an original document feeding unit is read. A shading correction for the image read by the first image reading mode is performed using a shading waveform generated by reading a first white plate. A shading correction for the image read by the second image reading mode is performed using a shading waveform generated by reading a second white plate.
According to Japanese Patent Laid-Open Publication No. 9-247395, a reading operation of a white plate is performed before reading an image of an original document with respect to a second original document thereafter. The reading operation of the white plate is carried out at a predetermined time either after a trailing edge of a preceding original document has passed between the white plate and a platen, or before a leading edge of a next original document abuts against the white plate.
As described above, two white plates are employed according to Japanese Patent Laid-Open Publication No. 8-9116, which increases the needed number of parts to be used, thereby resulting in an increase of man-hours needed to produce the device. The image reading device disclosed in Japanese Patent Laid-Open Publication No. 9-247395 cannot be used for a copying machine which can read an image of an original document either by a sheet-through mechanism or by putting the original document on a platen and covering it with a pressure plate, because an image reading position does not move in the image reading device.
With respect to synchronization between an image reading operation and an image output operation, for example, synchronization between an original document to be read and a transfer sheet is required in a copying machine. Image reading and writing operations are performed only after preparations of the original document and the transfer sheet have been completed. In a facsimile, synchronization between a preparation of an application for the facsimile and an image reading operation is required. It is necessary to effectively utilize a waiting time for synchronization so as to increase reading throughput, and an appropriate shading operation has to be performed in order to obtain a high quality image.
Furthermore, shading data for a next original document is obtained after an image of the preceding original document is read in the case of reading a plurality of original documents. However, when an operator switches, for example, an image quality mode before reading the image of the next original document, shading data for the next original document has to be acquired again.
The present invention has been made in view of the above-mentioned and other problems and addresses the above-discussed and other problems.
The present invention advantageously provides a novel image reading device and method in which an image of an original document is read either by a sheet-through mechanism or by placing the original document on a platen, with increased reading throughput.
The present invention also provides a novel image forming apparatus with increased reading throughput by performing a shading operation immediately after an image of an original document is read by a sheet-through mechanism.
The present invention further provides a novel image reading device and an image forming apparatus which perform a shading operation which sacrifices reading throughput when a switching of an image quality mode or a background removal mode is performed.
According to an embodiment of the present invention, an image reading device includes an exposure optical system configured to read an image of an original document conveyed on a platen at a fixed speed, a shading plate configured to be read for acquiring shading data used for correcting a white level of image information readout, a scanner carriage configured to move an image reading position of the exposure optical system for reading the shading plate, and a controller configured to control the scanner carriage such that the scanner carriage moves to a position where the shading plate is disposed so as to perform a shading operation before and after image reading operations of the original document are performed.